It is a dark green thing about 2-3 inch long we do not know it it is a worm or a caterpillar nor do we know if it is poison or not it also has sharp yellow spikes on its back. It whould be great if we found out what it is ;)

See if any of these caterpillars (http://www.ca.uky.edu/entomology/entfacts/ef003.asp) are a match. Also check the website of your local extension office. I brushed into a one of these critters when I was camping as a child and they are best avoided; the pain will curl you up into a ball.